In recent years, the notion of mounting large lithium-ion secondary batteries, having high energy density and excellent output energy characteristics, in electric vehicles has been investigated in response to increasing concern over environmental issues. In particular, lithium-ion secondary batteries for automobiles are difficult to replace at an intermediate stage due to their large size and high cost. Therefore, the lithium-ion secondary batteries for vehicles are required to have at least the same durability as that of vehicles and demanded to have a product life of 10 years or longer (high durability). When graphitic materials are used, there is a tendency for damage to occur due to crystal expansion and contraction caused by repeated lithium doping and de-doping, which diminishes the charge/discharge repetition performance. Therefore, such materials are not suitable as anode materials for lithium-ion secondary batteries for vehicles which require high cycle durability. In contrast, carbonaceous materials such as non-graphitizable carbon, of which the graphite structure does not reach a high degree, are suitable for use in automobile applications from the perspective of involving little particle expansion and contraction due to lithium doping and de-doping and having high cycle durability.
Furthermore, in the latest lithium-ion secondary batteries for vehicles, increased discharge capacity is required to extend the cruising range on a single charge and to improve vehicle fuel consumption. There is also a demand for increased discharge capacity per unit volume because of the need to reduce the installation space of the battery. A known means for increasing capacity is to promote the development of pores by performing heat treatment under reduced pressure or in a chlorine atmosphere in the manufacturing process of the carbonaceous material (Patent Documents 1, 2). However, the carbonaceous material manufactured by these methods has poor storage stability. In contrast, it has also been proposed to improve storage stability by increasing the amount of closed pores in the carbonaceous material (Patent Document 3), but this brings about the undesired result of greatly reducing capacity.